sedimentary

Limestone

Calcareous sedimentary rock (CaCO3)

Hardness: 3 on Mohs scale; Color: beige, light gray, tan, or white; Luster: dull to earthy; Crystal structure: microcrystalline or fine-grained; Cleavage: none (conchoidal fracture); Specific gravity: 2.7

Hardness: 3 on Mohs scale
Color: beige, light gray, tan, or white
Luster: dull to earthy

Identified August 6, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed by the accumulation of skeletal fragments from marine organisms such as coral, algal, and foraminifera, as well as chemical precipitation of calcium carbonate in shallow marine environments over millions of years.

Uses & applications

Used extensively in construction (aggregate, concrete, road base), manufacturing of cement, agriculture (soil conditioning), and as a building stone.

Geological facts

Limestone can host extensive cave systems formed by the dissolution of calcium carbonate by slightly acidic groundwater. Many of the world's most famous monuments and historical buildings, including the Great Pyramids of Giza, are made of limestone.

Field identification & locations

Can be easily identified in the field by its characteristic reaction to dilute hydrochloric acid, which causes it to fizz or effervesce vigorously due to the release of carbon dioxide.